c语言写入文件出现多余数据怎么办？

写入文件的函数如下

void savebookfile()
{
    book* pbook;
    pbook = bookhead;
    FILE* pbookfile = fopen("file\\bookfile.txt", "w");
    if (pbookfile == NULL)
        return 0;
    while (pbook)
    {
        fwrite(pbook, sizeof(book), 1, pbookfile);
        pbook = pbook->next;
    }
    fclose(pbookfile);
    return 0;
}

当我输入数据（1 1 1 1 1 1）后，文件保存了额外的东西，请问怎么才能解决？

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while (pbook->next）